Interpretive Summary: This manuscript describes a B. bovis gene coding for a protein with sequence similarity to the Toxoplasma gondii micronemal 1 (MIC1) protein that contains a copy of a domain described as a sialic acid-binding micronemal adhesive repeat that it is known to be involved in cell adhesion mechanisms. The B.bovis MIC1 protein is expressed by merozoites and elicits antibodies during B. bovis infection. Importantly, this study demonstrates that antibodies against the B. bovis MIC 1 protein can block invasion of erythrocytes by B. bovis. Together with its high degree of conservation among isolates, these features suggest that the B. bovis MIC1 protein may be considered a candidate for development of subunit vaccines.

Technical Abstract:
A gene coding for a protein with sequence similarity to the Toxoplasma gondii micronemal 1 (MIC1) protein that contains a copy of a domain described as a sialic acid-binding micronemal adhesive repeat was identified in the Babesia bovis genome. The single copy gene, located in chromosome 3, contains an open reading frame encoding a 181 amino acid protein, and is highly conserved among distinct B. bovis strains. The B. bovis-MIC1-like (Bbo-MIC1-like) protein is recognized by antibodies in serum from B. bovis infected cattle, demonstrating expression and immunogenicity during infection. Antibodies against both recombinant protein and synthetic peptides mimicking putative antigenic regions in the Bbo-MIC1-like protein significantly inhibit erythrocyte invasion in in vitro B. bovis cultures. B. bovis merozoites invade erythrocytes using a sialic acid-dependent mechanism, therefore, it is possible that Bbo-MIC1-like protein plays significant roles in host cell recognition and invasion and may be considered a candidate for development of subunit vaccines.